The present invention relates to an acoustic measurement system and method suitable for detecting solids in a fluid. More particularly, this invention relates to an improved acoustic mixing system which is able to detect the presence of various solids in a drilling fluid, and/or to measure the bulk modulus of the fluid, to provide valuable information relative to the drilling or production operation.
Acoustic measurement devices provide an excellent tool for the detection of solids in fluid systems, and may be particularly useful where the presence of the solids may pose problems to other measurement devices. Acoustic measurements may be utilized to detect the presence and/or occurrence of waxes, paraffins, asphaltenes, hydrates, and crystalline compositions within a fluid media. These measurements thus provide valuable information to, for example, an oil service company interested in drilling and/or production of oil from a subterranean formation. To improve measurement/determination accuracy and reliability, the fluid phases in a sampled media to be measured preferably may be stirred within the sample cell, substantially while making measurements, to suspend and disperse solid phases within the fluid phases. However, the accuracy of existing acoustic detection devices and methods are hampered by lack of adequate means for mixing a sample during detection measurements. The ineffectiveness of prior art approaches that have attempted to effectively mix samples within acoustic detection devices is illustrative of the problem.
One attempt to induce mixing has been to rock or otherwise rotate or move the sample cell. Studies have determined, however, that the mixing action achieved by such methods frequently may not provide appreciable measurement signal change as compared to a non-rocked measurement, and thereby does not sufficiently increase measurement accuracy. Such rocking or dynamic mechanism also may be cumbersome and may require special care for the tubings and electrical connections interconnected with the sample cell. Other mixing attempts have included providing a specially designed ring inside of the sample cell that could move inside of the cell while rocking the cell, thereby generating mixing within the cell. Mixing results generated by the ring device may also be inadequate. The ring also offers an increased opportunity for measurement signal distortion if the ring becomes cocked or wedged in the cell. The ring may also be deficient in introducing mixing action within the pores of a porous test media.
Other mixing techniques have included providing a mechanical stirrer inside of the measurement cell, which may in some instances result in improved mixing results as compared to rocking type mixing devices. Mechanical mixing devices, however, may increase the complexity and size dimensions of the measurement cell. In addition, invasive type mixing devices may create measurement distortions, undesirable sample disturbances, and may interfere with measurement results. Additional avenues for the occurrence of leaks at high pressures may also be included. Measurement apparatus and cell construction, fabrication, operation, expense, portability and versatility may also present additional problems and challenges with mechanical and other invasive type mixing devices, particularly for operations across a wide temperature and/or pressure spectrum.
The disadvantages of the prior art are overcome by the present invention, and an improved acoustic measurement device and method is hereinafter disclosed for reliably mixing materials within a measurement cell in order to more accurately detect the presence of solids within a fluid media, and/or to measure the bulk modulus of a fluid.
The present invention provides a method and system for more effectively mixing fluid media samples in an acoustic measurement cell to facilitate detection of solids in the fluid, or to measure the bulk modulus of the fluid. This invention is particularly applicable in measurements to detect the presence of waxes, paraffins, asphaltenes, hydrates and crystalline solids within the fluid, which may then provide valuable information to an oil or gas well drilling and/or production operation. More particularly, this invention may detect the presence of such solids in the rather unusual conditions of low temperature and high pressure, such as may be encountered in an offshore, deep-water environment. The invention may also be used to measure the bulk modulus of a pressurized fluid, thereby providing valuable information regarding the mixture of liquids and gas under high pressure conditions. System adaptability and portability render the invention highly flexible and easily upgradable, even for higher pressures and lower temperature than may be encountered in offshore, deep-water environments, such as in down-hole applications, geothermal applications, and in industries other than analysis of well fluid. The term xe2x80x9cfluidxe2x80x9d as used herein is intended to include Neutonian and non-Neutonian fluids, emulsions, gas-liquid mixtures, and fluids in the presence of solid media, such as within the pores of a rock sample.
It is an object of the present invention to provide an acoustic measurement system for detecting solids in the fluid, or for measuring the bulk modulus of the pressurized fluid, with the system including a sample cell for containing the fluid and a first acoustic transducer for outputting a first acoustic detection signal of a first frequency, and an ultrasonic receiver responsive to the first acoustic detection signal. A second acoustic transmitter is provided for outputting an acoustic second mixing signal at a second frequency to mix the solids in the fluid within the sample cell.
According to the method of the invention, ultrasonic measurements may be obtained under a variety of pressure and temperature conditions within a cell, with the frequency of the second ultrasonic mixing signal being significantly different than the frequency of the first acoustic detection signal. In an exemplary embodiment, the frequency of that first signal may between 500 kHz to 1 gHz, while the second signal may be 50 kHz or less.
It is a feature of the present invention that the ultrasonic measurement system is capable of simulating downhole conditions, and may be used to differentiate between a gas pocket and hydrate to determine how much hydrate is present, the size distribution of the solid particles within the fluid, and the kind of hydrate, e.g., methane or pentane.
It is a further feature of the invention that the first acoustic detection signals may be generated with both a longitudinal and a shear wave transducer.
Yet another feature of the invention is that the ultrasonic measurement system is able to measure the acoustic velocity of samples at various temperatures and pressures. Components of the samples may be one of multiple phases during measurement tests.
A further feature of the invention is that controller may be provided for regulating the xe2x80x9conxe2x80x9d time of the second transducer, and for detecting the first acoustic detection signals during xe2x80x9coffxe2x80x9d time of the second transducer.
Another feature of the invention is that the acoustic measurement system is able to reliably test fluids with fluid pressures in excess of 20,000 psi.
An advantage of the present invention is the ultrasonic measurement system may be used to calibrate sonic logs, or to differentiate between hydrates, gas pockets, shallow water flow zones, and other phenomenons.
It is a further advantage of the invention that the ultrasonic measurement system may be used to detect wax, asphaltene, crystallization, and/or hydrate.
A significant advantage of the method of the invention is the significantly reduced time required to conduct reliable measurements, along with the versatility when testing the fluid under various pressure and temperature conditions.